Drive sprocket

ABSTRACT

A drive sprocket comprising a plurality of teeth for meshing with a drive member to transmit rotary motion, the drive member including a plurality of engagement pockets engaging the teeth of the drive sprocket, wherein each tooth has a tooth profile defined by a first side comprising a first engagement surface and an opposite second side comprising a second engagement surface, which engagement surfaces are configured such that when driven, a tooth meshes to the engagement pocket at a first contact location on the first engagement surface and also at a second contact location on the second engagement surface, wherein the first contact location is radially offset from the second contact location.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part (CIP) application of U.S.patent application Ser. No. 16/629,918, filed Jan. 9, 2020, which is anational stage application of International Patent Application No.PCT/GB2018/000105, filed Jul. 10, 2018, which claims priority to GreatBritain Application No. 1711342.4, filed Jul. 13, 2017, Great BritainApplication No. 1715782.7, filed Sep. 28, 2017, and Great BritainApplication No. 1717436.8, filed Oct. 24, 2017, the disclosures of allof which are incorporated herein by reference in their entirety,including any figures, tables, and drawings.

BACKGROUND TO THE INVENTION

This invention relates to a drive sprocket, and particularly, but notexclusively, to a drive sprocket for use with a drive member, whereinthe drive sprocket comprises a plurality of teeth. The invention alsorelates to a transmission system comprising a drive sprocket and a drivemember, and a drive member forming part of a transmission system.

Drive sprockets, or pulleys, having a plurality of teeth for use withdrive members such as power transmission chains or belts are well known,and often take the form of a substantially circular sprocket having aplurality of teeth spaced apart around an outer circumference of thesprocket.

A variety of different drive members may be used with such drivesprockets.

A first type of known drive member is a power transmission chain in theform of a roller chain. The roller chain has a plurality of engagingformations for enabling engagement with the drive sprocket. The engagingformations are in the form of receiving formations, for receiving theteeth of the drive sprocket. An example of a use of a roller chain isfor a bicycle. The roller chain for a bicycle passes around a frontdrive sprocket in the form of a crank drive sprocket, and it also passesaround a rear drive sprocket in the form of a gear wheel. The knownroller chains are also able to be used in many other different types ofapparatus including, for example, tricycles, motorcycles and chain saws.

A second type of known drive member is a power transmission chaincomprising a silent chain. The silent chain also has a plurality ofengaging formations for enabling engagement with the drive sprocket. Theengaging formations are in the form of tooth formations for beingreceived in receiving recesses formed between adjacent teeth on thedrive sprocket. The silent chain is used for high torque applicationswhich need high efficiency and the transfer of a lot of power.

Typical of such applications is the use of a silent chain as a timingchain for engines. The silent chain is also often referred to as a HY-VOchain.

A third type of know drive member is a belt which is adapted to engagewith the teeth of a sprocket.

As is well known, a drive member enables transmission of power betweendrive sprockets. Known drive sprockets may drive the drive member as inthe case of a front sprocket drive sprocket on a bicycle, or the drivesprockets may be driven by the drive member as in the case of rear geardrive sprockets on a bicycle.

It is known that power transmission chains are formed by chain linkswhich are pivotally contacted together by pivots which extendtransversely completely across the chain link.

The known drive members and known drive sprockets do not transmit poweras efficiently as would be desired. More specifically, the known drivemembers invariably make contact with the drive sprockets undersignificant loads, and in such situations, the drive members frequentlytend to move relative to the teeth of the sprocket whilst maintainingcontact under this high loading. The result is that the known powertransmission chains do not work efficiently on the drive sprockets.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided adrive sprocket comprising a plurality of teeth for meshing with a drivemember to transmit rotary motion, the drive member including a pluralityof engagement pockets engaging the teeth of the drive sprocket, whereineach tooth has a tooth profile defined by a first side comprising afirst engagement surface and an opposite second side comprising a secondengagement surface, which engagement surfaces are configured such thatwhen driven, a tooth meshes to the engagement pocket at a first contactlocation on the first engagement surface and also at a second contactlocation on the second engagement surface, wherein the first contactlocation is radially offset from the second contact location.

By means of the present invention, during use of the drive sprocket,each tooth of the sprocket will engage with the drive member at twocontact locations on opposite sides of each tooth. In addition, thefirst contact location will, during use be radially offset from thesecond contact location.

Such an arrangement reduces the stress on the sprocket during usethereby reducing the wear and tear on the drive sprocket as well as thefrictional losses, thereby increasing transmission efficiency.

In addition, the radial offset of the first and second contact locationshelps to prevent the engagement pocket of the drive member from becomingwedged, or stuck, on a tooth during use of the drive sprocket.

By means of the present invention, therefore, secure engagement of thepitch pocket with the tooth may be achieved as the drive member makescontact with the drive sprocket. In addition, the stress on the drivesprocket as the load is transferred between the drive sprocket and thedrive member is distributed to reduce localised peak stresses. Further,disengagement of the pitch pocket from the tooth may be reliablyachieved.

In embodiments of the invention, each tooth has a front face and a backface, the shape of which front and back faces being defined by the firstand second sides, wherein the shape of each face is symmetrical about aradial axis of the tooth, and the sides of the faces are defined atleast partially by two arcs. An advantage of having a tooth where theshape of the front and back faces is symmetrical, is that it is possiblefor the drive sprocket to rotates in both a forward and a reversedirection. A symmetric tooth also enables applications with only onedrive direction to handle torque reversal during operation. This resultsin the drive sprocket being more adaptable to different uses.

In embodiments of the invention, each arc defines a side of a tooth andhas a radius of R, the centres of the arcs being at a distance x fromone another, and at a perpendicular distance, y, from the centre of thedrive sprocket, and wherein the centre of each arc is at ±x/2,y.

In embodiments of the invention, adjacent teeth are spaced apart fromone another by a connecting portion of the sprocket.

In such embodiments of the invention, the tolerance of a transmissionsystem incorporating a drive sprocket according to embodiments of theinvention to dimensional variations within the system's components willbe increased.

According to a second aspect of the present invention there is provideda transmission system comprising a drive sprocket according toembodiments of the first aspect of the invention, and further comprisinga drive member, which drive member is adapted to engage with the drivesprocket.

In embodiments of the invention, the drive member comprises a pluralityof engagement pockets, each of which engagement pockets comprises afirst engaging surface and a second engaging surface spaced apart fromthe first engaging surface, the first and second engaging surfacesforming an engagement surface pair, which pair is rotatable about arotational axis, wherein adjacent engagement pockets are connected toone another by connecting members.

In embodiments of the invention, adjacent engagement pockets areconnected to one another by a primary link, which primary link isrotatable about the rotational axis of the engagement surface pair.

In such embodiments of the invention, the drive member may engage withthe teeth of the drive sprocket, such that each engagement pocket isadapted to receive a tooth of the drive sprocket and to engage with thetooth at first and second engaging surfaces. Because adjacent engagementpockets are connected to one another by a primary link which isrotatable about the rotational axis of the engagement surface pair, thetooth will thus mesh to the engagement pocket such that the firstcontact location engages with the first engaging surface, and the secondcontact location engages with the second engaging surface.

The tooth is thus securely held by the engagement pocket such thatlittle or no movement of the tooth relative to the pocket is possibleonce the tooth has meshed to the engagement pocket. In addition, becausethe first and second contact locations are radially offset relative toone another during use of the transmission system, the tooth is lesslikely to become stuck, or wedged in the engagement pocket compared towhen there is no radial offset.

In embodiments of the invention, each primary link is rotatable aboutthe rotational axis of each adjacent engagement pocket. This facilitatesthe articulation of the drive member.

In embodiments of the invention, the drive member comprises a pluralityof first primary links which are coplanar with one another and arepivotally connected to one another at first and second pivot points,which pivot points are spaced apart from one another such that adjacentfirst primary links are pivotable about the axis of rotation of eachadjacent engagement pocket.

Such an arrangement may be desirable when the drive member comprises apower transmission chain, for example.

In embodiments of the invention, the drive member comprises a pluralityof second primary links coplanar with one another and pivotallyconnected to one another at first and second pivot points, which pivotpoints are spaced apart from one another such that adjacent secondprimary links are pivotable about the axis of rotation of each adjacentengagement pocket, wherein the first primary links are connected to thesecond primary links such the first and second primary links aresubstantially parallel to one another, and the first pivot points of thefirst links are coaxial with the second pivot points of the secondlinks, and the second pivot points of the first links are coaxial withthe first pivot points of the second links.

In embodiments of the invention, each engagement pocket comprises firstand second transverse members each having a first end and a second end,the first and second transverse members being spaced apart from oneanother, wherein the first and second engaging surfaces are formed onthe first and second transverse members respectively.

In such embodiments, the secondary links may be parallel with theprimary links, and the transverse members may be substantiallyperpendicular to the primary and secondary links.

In embodiments of the invention, each engagement pocket comprises afirst secondary link positioned at, or close to the first ends of thefirst and second transverse members, and a second secondary linkpositioned at, or close to the second ends of the transverse members,wherein the first and second secondary links are parallel with oneanother.

In such embodiments of the invention, first and second secondary linksmay be positioned opposite one another with the first and secondtransverse members extending substantially parallel to one another andsubstantially perpendicularly to the first and second secondary links.Each engagement pocket is thus defined by the first and second secondarylinks and the first and second transverse members.

In embodiments of the invention, the first and second transverse memberseach have a radius r, wherein the distance between the first and secondtransverse members of an engagement pocket is p2, and the distancebetween first and second pivot points of a primary link is p.

In embodiments of the invention the first and second transverse memberscomprise first and second rollers respectively, each of which first andsecond rollers may have a radius r and may be rotatable about theirrespective axes. In other embodiments, the first and second transversemembers may comprise first and second pins respectively, each of whichfirst and second pins may have a radius of r and may not be rotatable.In still other embodiments, the first and second transverse memberscomprise first and second curved surfaces each surface having a radiusof curvature of r.

According to a third aspect of the invention, there is provided a drivemember forming part of a transmission system according to embodiments ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be further described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a schematic representation of a drive sprocket according to anembodiment of the first aspect of the invention;

FIG. 2 is a detailed representation of a part of the drive sprocket ofFIG. 1 ;

FIG. 3 is a schematic representation of the drive sprocket of FIGS. 1and 2 engaged with a drive member according to embodiments of the thirdaspect of the invention and comprising a power chain, to form atransmission system according to embodiments of the second aspect of theinvention;

FIG. 4 is a more detailed schematic representation of the transmissionsystem of FIG. 3 ;

FIG. 5 is a schematic representation of the transmission system of FIGS.3 and 4 with the primary links from one side removed;

FIGS. 6, 7 and 8 are schematic representations of part of thetransmission system as shown in FIG. 5 showing the position of thesecondary links during rotation of the drive sprocket;

FIGS. 9 and 10 are schematic representations showing dimensions of theprimary and secondary links of the transmission chain;

FIG. 11 is a schematic representation showing the position of the arccentres defining the sides of the teeth of the drive sprocket relativeto the centre of the drive sprocket;

FIG. 12 is a schematic representation showing the radial offset of thefirst and second contact locations of a tooth of the drive sprocket ofFIG. 1 ; and,

FIG. 13 is a schematic diagram showing the dimensions of the drivesprocket shown in FIGS. 1 and 2 .

DETAILED DESCRIPTION

Referring initially to FIGS. 1 and 2 , a drive sprocket according to anembodiment of the first aspect of invention is designated generally bythe reference numeral 10.

The sprocket 10 comprises a plurality of teeth 12 that are spaced apartfrom one another around an outer circumference 14 of the sprocket 10.

Each tooth has a tooth profile defined by a first side 16 comprising afirst engagement surface 18, and an opposite second side 20 comprising asecond engagement surface 22. Each tooth further comprises a front face24 and a back face 26, the shape of which faces being defined by thefirst and second sides 18, 20, which in this embodiment comprise firstand second engagement surfaces. The shape of each face is symmetricalabout a radial axis 28 extending along the length of each tooth.

The shape of each side 16, 20 is defined at least partially by an arc.Because each tooth 12 is symmetrical about the axis 28, the dimensionsof the arcs forming all sides is the same.

Referring now to FIG. 11 , it can be seen that in this embodiment, eacharc defining a side of a tooth 12 has a radius of R. The centres of thearcs are at a distance x from one another, and at a perpendiculardistance y, from the centre of the drive sprocket. The centre of eacharc is at ±x/2,y. Adjacent teeth 12 are separated from one another todefine a connecting portion 30, as shown in FIG. 2 , for example. In theillustrated embodiment, the connecting portion is substantially flat.However, it is to be understood that in other embodiments of theinvention the connecting portion may not be flat, or there may not be aconnecting portion at all.

Turning now to FIGS. 3 to 8 , a transmission system according to anembodiment of the second aspect of the invention is designated generallyby the reference numeral 100. The transmission system 100 comprises thesprocket 10 illustrated in FIGS. 1 and 2 and described hereinabove. Thetransmission system 100 further comprises a power transmission chain110. The power transmission chain 110 is adapted to engage with thesprocket 10 as will be described hereinbelow in order to enabletransmission of power between the drive sprocket 10 and another drivesprocket (not shown).

As shown particularly in FIGS. 6, 7 and 8 for example, the powertransmission chain 110 comprises a plurality of engagement pockets 150extending along the chain 110. Each engagement pocket 150 comprises afirst engaging surface 152, and a second engaging surface 154 which isspaced apart from the first engaging surface 152. The first and secondengaging surfaces 152, 154 together form an engaging surface pair 156.

Each engaging surface pair 156 is rotatable about a rotational axis 158.Adjacent engagement pockets 150 are connected to one another by at leastone primary link 112, which primary link 112 is rotatable about therotational axis 158.

In this embodiment there is a set of first primary links 114 which areco-planar with one another, a set of second primary links 116 which areco-planar with one another, a set of third primary links 118 which areco-planar with one another and a set of fourth primary links 120 whichare also co-planar with one another. Each set of primary links issubstantially parallel with each other set of primary links.

The primary links 112 in a particular set, which are co-planar to oneanother, are also pivotally connected to one another. Each primary link112 has a first pivot point 122, and a second pivot point 124, the firstand second pivot points 122 and 124 being spaced apart from one anotheralong each primary link 112, such that adjacent primary links 112 arepivotable about the first and second primary pivot points 122, 124.

In the illustrated embodiment of the invention, the first 114 and second116 primary links are connected to and abut one another such that thefirst pivot point 122 of a first primary link 114 is coaxial with thesecond pivot point 124 of a second primary link 116, and vice versa.

Similarly, the third 118 and fourth 120 primary links are connected toand abut one another such that the first pivot point 122 of a thirdprimary link 118 is coaxial with the second pivot point 124 of a fourthprimary link 120, and vice versa.

The power transmission chain 110 further comprises a plurality ofsecondary links 130 each of which secondary links is adapted to rotatesubstantially about the rotational axis 158 of the respective engagementpocket 150. Each secondary link 130 is positioned to be substantiallyparallel with a respective primary link 112 such that the rotationalaxis 158 of a particular engagement pocket 150 is coaxial with the first122, or second 124, pivot points of the corresponding primary links 112.This in turn means that adjacent primary links 112 are pivotable aboutthe axis of rotation 158.

In this embodiment, the plurality of secondary links 132 comprises aplurality of first secondary links 138, and a plurality of secondsecondary links 140. Each first secondary link 138 abuts a secondprimary link 116, and each second secondary link 140 abuts a thirdprimary link 118.

In this embodiment, two first secondary links 138 abut each secondprimary link 116, and two second secondary links 140 abut each thirdprimary link 118.

In this embodiment of the invention, the first secondary links 138 aresubstantially coplanar with one another, and the second secondary links140 are substantially coplanar with one another, the first secondarylinks 138 are spaced apart from the second secondary links 140 such thateach first secondary link 138 faces a corresponding second secondarylink 140 to form a pair of secondary links 142.

In this embodiment, each engagement pocket 150 comprises first andsecond transverse members 144, 146, which are spaced apart from oneanother and on which the first and second engaging surfaces 152, 154respectively, are formed. The first and second transverse members 144,146 extend transversely between the corresponding first and secondsecondary links forming the pair. The transverse members 144, 146 thusconnect the secondary links together. In this embodiment, the first andsecond transverse members 144, 146 each comprise a roller 148. In otherembodiments, each transverse member 144, 146 may comprise a pin.

The space defined between the first and second transverse members of asecondary link forms an engagement pocket 150. The engagement pockets150 are shaped and positioned to receive and engage with a tooth 12 ofthe sprocket 10, as shown in the Figures.

In use of the transmission system 100, a tooth 12 of the drive sprocket10 will mesh to the engagement pocket 150 at a first contact location160 on the first engagement surface 18 and also at a second contactlocation 162 on the second engagement surface 20, as shown in FIG. 6 ,for example. Once engaged, the first contact location 160 will engagewith the first engaging surface 152 of the engagement pocket 150, andthe second contact location 162 will engage with the second engagingsurface 154 of the engagement pocket 150.

Due to the inter-relationship between the primary links and secondarylinks as explained hereinabove together with the transverse members 144,146 and the features of the drive sprocket 10, during use of thetransmission system 100 the first contact location 160 is radiallyoffset from the second contact location 162.

This in turn results in the rollers 148 maintaining contact with thefirst and second engagement surfaces 18, 20 of each corresponding tooth12, and each secondary link 130 sitting at an offset angle such that oneroller 148 sits radially higher on one side the tooth 12 than the roller148 on the other side of the tooth.

The geometry of the teeth 12 and of the transmission chain 110 will nowbe described in more detail with particular reference to FIGS. 9 to 13 .

Referring initially to FIGS. 9 and 10 a portion of the transmissionchain 110 is illustrated schematically.

As can be seen, the distance between first and second p pivot points122, 124 of a primary link 112 is p, the distance between the axes offirst and second transverse members 144, 146 is p₂, and the radius ofeach roller 148 is r.

Referring now to FIG. 11 , according to Cartesian coordinates where theorigin is at the sprocket centre and the centreline of the tooth isparallel with the y axis:

A symmetrical tooth geometry is proposed with two arcs of radius R witharc centres at

$\left( {{\pm \frac{x}{2}},y} \right),$where, R, x, & y are defined such that when the chain is articulatedaround the sprocket and a load is applied to the chain:

-   -   1. the rollers of each secondary link maintain contact with the        two arcs of each corresponding tooth, and;    -   2. the secondary links sit at an offset angle such that one        roller sits higher on one side of the tooth than the roller on        the other side of the tooth.

Furthermore, straight lines of length l extend above the tooth from theends of the arcs towards the centreline at an angle, γ, relative to thetooth centreline such that as the chain wears, causing the pitch, p, ofthe chain to elongate and the corresponding pitch circle radius, r_(p),to increase:

-   -   1. contact can be maintained with the tooth by both rollers,        and;    -   2. the normal contact force acting on the load-bearing upper        roller remains parallel to the tensile force in the primary link        on the high-tension side of the chain.

Referring now to FIGS. 12 and 13 , the geometry of the sprocket will beconsidered in more detail.

Equations 1 & 2 below give α, the angle of articulation, and r_(p), thepitch circle radius, for an n-toothed sprocket of pitch p.

$\begin{matrix}{\alpha = \frac{\pi}{n}} & (1) \\{r_{p} = \frac{p}{2\;\sin\;\alpha}} & (2)\end{matrix}$

The values of the arc parameters, R, x & y are given by the solutions tothe set of simultaneous equations given by Equations 3 to 6, where

$\begin{matrix}{{\gamma = {\alpha + \varphi}},{{{{{0 < \delta < \gamma}\&}\gamma} < \beta < {\frac{\pi}{2} - {\alpha.R}}} = {r + \frac{p_{2}\sin\;\delta}{{\sin\;\beta} - {\sin\;\gamma}}}}} & (3) \\{x = {{\left( {R - r} \right)\left( {{\cos\;\gamma} + {\cos\;\beta}} \right)} + {p_{2}\;\cos\;\delta}}} & (4) \\{\varphi = {\sin^{- 1}\left( \frac{{2\left( {R - r} \right)\cos\;\gamma} + {p_{2}\cos\;\delta} - x}{2\; r_{p}} \right)}} & (5) \\{y = {{r_{p}\cos\;\varphi} + {\left( {R - r} \right)\sin\;\gamma} + {\frac{p_{2}}{2}\sin\;\delta}}} & (6)\end{matrix}$

TABLE 1 Example values for R, x & y given p, p2, r, n, β & δ ChainGeometry p 12.7 mm p2 7.5 mm r 3 mm General Sprocket Geometry n 19 α0.165 rad rp 38.58 mm Tooth Geometry Parameters β 0.262 to 1.466 rad δ0.021 to 0.102 rad Tooth Geometry R 1.68 to 6.62 mm x  7.69 to 17.50 mmφ 0.0002 to 0.0065 rad y 60.85 to 61.68 mm

What is claimed is:
 1. A drive sprocket comprising a plurality of teethfor meshing with a drive member to transmit rotary motion, the drivemember including a plurality of engagement pockets engaging the teeth ofthe drive sprocket, wherein each tooth has a tooth profile defined by afirst side comprising a first engagement surface and an opposite secondside comprising a second engagement surface, which engagement surfacesare configured such that when driven, a tooth meshes to the engagementpocket at a first contact location on the first engagement surface andalso at a second contact location on the second engagement surface,wherein the first contact location is radially offset from the secondcontact location.
 2. The drive sprocket according to claim 1, whereineach tooth has a front face and a back face, the shape of which facesbeing defined by the first and second sides, wherein the shape of eachface is symmetrical about a radial axis of the tooth, and the sides ofthe faces are defined at least partially by two arcs.
 3. The drivesprocket according to claim 2, wherein the two arcs each have a radiusof R, the centres of the arcs being at a distance x from one another,and at a perpendicular distance, y, from the centre of the drivesprocket, and wherein the centre of each arc is at ±x/2,y.
 4. The drivesprocket according to claim 1, wherein adjacent teeth are spaced apartfrom one another to define a connecting portion of the sprocket.
 5. Atransmission system comprising: a drive sprocket; and a drive member,which drive member is adapted to mesh with the drive sprocket, whereinthe drive sprocket comprises a plurality of teeth for meshing with thedrive member to transmit rotary motion, wherein the drive memberincludes a plurality of engagement pockets engaging the teeth of thedrive sprocket, wherein each tooth has a tooth profile defined by afirst side comprising a first engagement surfaces are configured suchthat when driven, a tooth meshes to the engagement pocket at a firstcontact location on the first engagement surface and also at a secondcontact location on the second engagement surface, and wherein the firstcontact location is radially offset from the second contact location. 6.The transmission system according to claim 5, wherein the secondengaging surface is spaced apart from the first engaging surface, thefirst and second engaging surfaces forming an engagement surface pair,which pair is rotatable about a rotational axis, wherein adjacentengagement pockets are connected to one another by a connecting member.7. The transmission system according to claim 6, wherein adjacentengagement pockets are connected to one another by a primary link, whichprimary link is rotatable about the rotational axis of the engagementsurface pair.
 8. The transmission system according to claim 7, whereineach primary link is rotatable about the rotational axis of eachadjacent engagement pocket.
 9. The transmission system according toclaim 7, comprising a plurality of first primary links which arecoplanar with one another and are pivotally connected to one another atfirst and second pivot points, which pivot points are spaced apart fromone another such that adjacent first primary links are pivotable aboutthe axis of rotation of each adjacent engagement pocket.
 10. Thetransmission system according to claim 9, comprising a plurality ofsecond primary links coplanar with one another and pivotally connectedto one another at first and second pivot points, which pivot points arespaced apart from one another such that adjacent second primary linksare pivotable about the axis of rotation of each adjacent engagementpocket, wherein the first primary links are connected to the secondprimary links such the first and second primary links are substantiallyparallel to one another, and the first pivot points of the first linksare coaxial with the second pivot points of the second links, and thesecond pivot points of the first links are coaxial with the first pivotpoints of the second links.
 11. The transmission system according toclaim 7, wherein each engagement pocket comprises first and secondtransverse members, each having a first end and a second end, the firstand second transverse members being spaced apart from one another,wherein the first and second engaging surfaces are formed on the firstand second transverse members respectively.
 12. The transmission systemaccording to claim 11, wherein each engagement pocket comprises asecondary link connecting the first and second transverse members,wherein the secondary links are coplanar with one another.
 13. Thetransmission system according to claim 12, wherein the secondary linksare parallel with the primary links, and the transverse members aresubstantially perpendicular to the primary and secondary links.
 14. Thetransmission system according to claim 12, wherein each engagementpocket comprises a first secondary link positioned at, or close to thefirst ends of the first and second transverse members, and a secondsecondary link positioned at, or close to the second ends of thetransverse members, where in the first and second secondary links areparallel with one another.
 15. The transmission system according toclaim 14, wherein each engagement pocket comprises a first set of firstand second primary links which are proximate the first secondary links,and a second set of primary and secondary links with are proximate thesecond secondary links.
 16. The transmission system according to claim15, wherein the first and second transverse members each have a radiusr, wherein the distance between the first and second members of anengagement pocket is p2, and the distance between first and second pivotpoints of a primary link is p.